by aero280 » May 1st, 2018, 2:19 pm
The amount of chlorine in tapwater can vary a lot. It depends on the source, and the regulations. When I retired, it was being replaced, but the new systems, UV light and ozone, were still under development.
If your water comes from a chalk or gravel aquifer via borehole pump, there is likely to be very little disinfection required.
If your water comes from rivers or other surface water, then it usually needs more disinfection because the incoming water quality varies enormously. Where I worked in London the water was mostly river derived, the technique was to assume the worst incoming quality and dose with chlorine to deal with that. Then the treated water was monitored for the amount of residual chlorine. If it was above the level needed, it was reduced by the addition of sulphur dioxide and ammonia.
But then things get a bit more complicated, because the EU regs required the minimum chlorine level to reach the furthest tap once a month, so the chlorine level will never be constant over time.
As a rough guide, and things change, you can use the water company owner as an indicator of the chlorine. In the past, all water was supplied commercially, and pumped from the ground or the river to the user. Once it became clear that river water was not drinkable without treatment, those sources became unprofitable and the companies folded and were taken over by Water Boards run by local authorities. In 1975 the Water B Boards were merged into Water Authorities. But the old Water Companies remained independent and profitable. So if your water comes from one of the ten old water authorities in England & Wales it will probably have more chlorine thatn water from one of the old water companies.
For example, if your water is supplied by Thames Water, Southern Water, Severn Trent, Yorkshire Water, etc. it will most likely be more chlorinated than if it comes from a private company. Private companies are ones like Affinity Water, Portsmouth Water, Mid Sussex, etc.